Volume 121
`Number 2
`
`Clinical and laboratory observations
`
`259
`
`Plasma glutamine concentration: A guide in the
`
`management of urea cycle disorders
`
`NancyE.MaefimPm1KafluynD.McGowan,MDhandSauHN.&uwow,MD
`From the Department of Pediatrics, Johns Hopkins School of Medicine, Baltimore, Maryland
`
`Because increases in plasma glutamine concentrations are almost always as-
`sociated with hyperammonemia in patients with urea cycle disorders, we deter-
`mined the correlation between these two variables for 2 years in a child with or-
`nithinetranscarbamylase deficiency. Acorrelation coetficientot 0.77 (p<0.0001)
`was found. Hyperammonemia was rarely observed when plasma glutamine
`levels were near normal. These data suggest that one goal of therapy is the
`maintenance of plasma glutamine levels at or near normal values. (J PEDIATR
`1992;121:259-61)
`
`
`
`The presence of hyperglutaminemia in hyperammonemic
`patients with urea cycle disorders has been known since the
`earliest case reports‘ and is another manifestation of the
`disorder of nitrogen homeostasis?’ 3 Moreover,
`in two
`patients with ornithine transcarbamylase deficiency, plasma
`glutamine levels increased before the onset of hyperam-
`monemia.4 Hyperglutaminemia is also associated with the
`hyperammonemia of severe liver disease5 and Reye syn-
`drome.6 On the basis of these observations,
`this study
`examined the relationship between the plasma glutamine
`and ammonium concentrations during a 24-month period in
`one patient with the neonatal form of OTC deficiency.
`CASE REPORT
`
`The patient was the younger brother of a boy with OTC
`deficiency who, after rescue from neonatal hyperammonemic
`coma, was profoundly developmentally delayed and died in hyper-
`ammonemic coma at age 16 months of age. The mother was iden-
`tified as a carrier of the mutation at the OTC locus on the basis of
`
`the diagnosis of the proband and a positive protein tolerance test
`result. More recently, the mutation in this pedigree has been iden-
`tified as a T—>C substitution in the initial dinucleotide of intron 7,
`resulting in a deletion of exon 7.7 The family was lost to follow-up
`until the mother was 26 weeks’ pregnant with a fetus of unknown
`
`Supported by National Institutes of Health grants HD 11134, HD
`26358, and RR 00052, U.S. Food and Drug Administration grant
`No. FD-R-000198, the T. D. and M. A. O’Malley Foundation, and
`the Kettering Family Foundation.
`Submitted for publication Nov. 15, 1991; accepted Feb. 25, 1992.
`Reprint requests: Saul W. Brusilow, MD, Department of Pediat-
`rics, Johns Hopkins School of Medicine, 600 N. Wolfe St., Park
`Building Room 336, Baltimore, MD 21205.
`*Now at the Department of Obstetrics and Gynecology, Johns
`Hopkins School of Medicine, Baltimore, MD 21205.
`9/22/37448
`
`gender. After genetic counseling, during which the options for di-
`agnosis and treatment were described, 3 the family chose delivery
`at their local community hospital and declined to enter the infant
`into an experimental diagnostic and treatment protocol. After de-
`livery, notwithstanding the earlier decision, the apparently healthy
`term male neonate was not fed enterally but was given only intra-
`venous fluids including 10% glucose solution. On discharge from
`the community hospital when the infant was 48 hours of age, the
`parents chose to seek therapy and the patient was brought directly
`to Johns Hopkins Hospital. On arrival he was lethargic and had
`plasma ammonium and glutamine levels, respectively, of 117 and
`2074 [£11101/L (normal values <30 and 613 i 15)9; plasma citrul-
`line was undetectable. He also had a plasma orotate level of 2.13
`
`OTC Ornithine transcarbamylase
`
`umol/ L (undetectable in normal neonates [Brusilow SW: unpub-
`lished observations]) and a respiratory alkalosis. After further
`counseling, the parents gave informed consent for the patient’s en-
`try into a study evaluating the intravenous dosage form of benzoate
`and phenylacetate, and long-term therapy with the oral dosage
`form of sodium phenylbutyrate. At 24 and 48 hours after intrave-
`nous therapy,1° the patient’s plasma ammonium levels were,
`respectively, 31 and 24 /.zmol/ L.
`In the subsequent 2 years the patient has been treated with a low
`protein diet (at times supplemented with essential amino acids),
`L-citrulline, 175 mg/kg per day, and sodium phenylbutyrate, 500
`to 600 mg/kg per day. The details and variations of this protocol
`are described elsewhere.” On the Cattell Infant Intelligence Scale
`his development quotient was 80 at 19 months of age. The patient
`is at the 25th percentile for weight and below the 3rd percentile for
`height. He has been admitted to the hospital three times because
`of symptomatic hyperammonemia.
`
`METHODS
`
`During the 2-year follow-up period, 57 measurements
`were made of plasma ammonium and amino acid levels. In-
`
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`2 6 0
`
`Clinical and laboratory observations
`
`The Journal of Pediatrics
`August 1992
`
`2400
`
`2 ‘IOO
`
`1800
`
`1500
`
`1200
`
`900
`
`600
`
`300
`
`
`
`
`
`PlasmaGlutamine(uM)
`
`
`
`60
`
`90
`
`120
`
`150
`
`Plasma Ammonium (uM)
`
`
`
`Figure. Relationship between plasma glutamine and ammonium concentrations. For all values the Pearson correlation
`coeflicient is 0.77 (p <0.0001). For plasma ammonium values less than 30 umol/ L (p = 0.436; p <0.0001).
`
`cluded in this study are those values obtained during all
`outpatient visits. Plasma ammonium levels were measured
`by a cation exchange—visible spectrophotometric tech-
`nique,“ and plasma amino acids were measured by auto-
`mated column chromatography using a Beckman model
`6300 amino acid analyser (Beckman Instruments, Inc.,
`Brea, Calif.). Apart from the initial sample, blood was col-
`lected from the patient during daytime hours (plasma glu-
`tamine levels are lowest then in patients treated with this
`protocol”). Blood was placed in hepaririized tubes and im-
`mediately chilled on ice, and the plasma was promptly sep-
`arated in a refrigerated centrifuge and analyzed immedi-
`ately or frozen for analysis within 24 hours.
`
`RESULTS
`
`The relationship between plasma levels of ammonium
`and glutamine in this patient is shown in the Figure. The
`Pearson correlation coeflicient for all values of glutamine
`and ammonium was calculated as 0.77 (p <0.0001). When
`plasma ammonium levels were within the normal range
`(<30 [£11101/L), glutamine levels varied between 145 and
`1090 [.LI1'10l/ L and were more weakly correlated with plasma
`ammonium levels (p = 0.436; p <0.0001).
`Plasma glutamine measurements were grouped into six
`strata, and the mean glutamine andéaflimonium levels were
`calculated. As shown in the Table, the mean ammonium
`level was normal for glutamine values less than 800 pmol/ L;
`however, when plasma glutamine levels increased above this
`level, an increasing percentage of ammonium levels were
`
`high. Furthermore, the height of the plasma ammonium
`, level was strongly correlated with the height of the plasma
`glutamine concentration.
`
`DISCUSSION
`
`The findings of a weaker correlation between plasma
`ammonium and glutamine levels when plasma ammonium
`levels are normal are consistent with the hypothesis that in-
`creased plasma glutamine levels are forerunners of in-
`creased plasma ammonium levels.‘‘ These data, in conjunc-
`tion with the reports cited earlier, suggest that glutamine
`may represent a storage site for nitrogen accumulation. The
`precise capacity of glutamine to serve this function is
`unknown, but it appears that as plasma glutamine levels in-
`crease to greater’than normal, there is a greater likelihood
`of hyperammonemia. Although the plasma level of glu-
`tamine above which ammonium accumulated in this patient
`was approximately 1000 amol / L, our random observations
`of other patients suggest, as might be expected, that there
`may be considerable individual variability of this threshold.
`These data have potentially useful monitoring and ther-
`apeutic implications. They suggest that increasing plasma
`glutamine levels may indicate that dietary or drug therapy
`requires modification. Such modifications include an in-
`creased dose of phenylbutyrate, an increased calorie intake,
`a reduction of total nitrogen intake, and redistribution of
`nitrogen intake between natural protein and essential amino
`acids to take advantage of the lower nitrogen density of es-
`sential amino acids.
`
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`

`Volume 121
`Number 2
`
`Clinical and laboratory observations
`
`261
`
`Table. Number of high (>30 umol / L) plasma ammonium levels for specified plasma glutamine levels
`
`Range of Gln
`(umol/L)
`200-400
`401-600
`601-800
`801-1000
`1001-1400
`>1400
`
`n
`12
`16
`13
`5
`7
`4
`
`Mean Gln
`(,umo|,lL)‘
`295 : 62.8
`503 : 61.3
`690 : 51.8
`892 -_= 66.8
`1190 : 84.0
`1829 : 302.8
`
`Mean NH4+
`(gmol/L)’
`
`21.8 1 7.0
`21.3 : 4.8
`21.5 i 4.1
`34.8 J_- 15.4
`55.0 : 36.3
`110.8 -_= 40.4
`
`Gln, Glutamine; NH4+, ammonium.
`*Values are mean i SD.
`
`NH4+ >30 nmol/L
`
`No.
`
`1
`1
`O
`2
`6
`4
`
`“lo
`
`8
`6
`O
`40
`86
`100
`
`
`
`cirrhosis: relation to other manifestations of liver disease.
`Gastroenterology 1978;75:570-9.
`. Romshe CA, Hilty MD, McClung J, Kerzner B, Reiner CB.
`Amino acid pattern in Reye’s syndrome: comparison with
`clinically similar entities. J PEDIATR 1981;98:788-90.
`Carstens RP, Fenton WP, Rosenberg LF, Identification of
`RNA splicing errors resulting in ornithine transcarbamylase
`deficiency. Am J Hum Genet l99l;48:l 105-14.
`. Maestri NE, Hauser ER, Bartholomew D, Brusilow SW. Pro-
`spective treatment of urea cycle disorders. J PEDIATR 1991;
`1 19:923-8.
`Batshaw ML, Brusilow SW. Asymptomatic hyperammonemia
`in low birth weight infants. Pediatr Res 1978;l2:221-4.
`Brusilow SW. Treatment of urea cycle disorders. In: Desnick
`R, ed. Treatment of genetic diseases. New York: Churchill
`Livingstone 1991 :79-94.
`Brusilow SW. Determination of urine orotate and orotidine
`and plasma ammonium. In: Hommes FA, ed. Techniques in
`diagnostic human biochemical genetics. New York: Wiley
`Liss, 19912345-57.
`Brusilow SW. Phenylacetylglutamine may replace urea as a
`vehicle for waste nitrogen excretion. Pediatr Res 1991;29:147-
`50.
`
`These findings may have broader significance in view of
`recent reports suggesting that glutamine may be more
`closely related to the pathophysiology of the encephalopa-
`thy of hyperammonemia than is ammonium”, 14
`
`We thank the nursing staff of the pediatric clinical research unit
`for their help in obtaining plasma specimens. We also thank Mrs.
`Ellen Gordes for her expert technical assistance in performing
`measurements of plasma ammonium.
`
`REFERENCES
`
`1.
`
`2.
`
`Levin B, Oberholzer VG, Sinclair L. Biochemical investiga-
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`. Arn PH, Hauser ER, Thomas GH, Herman G, Hess D, Brusi-
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`Hawkins RA, Jessy J. Hyperammonemia does not impair brain
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`Takahashi H, Koehler RC, Brusilow SW, Traystman RJ. In-
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